Power devices that have a double-diffused Metal-Oxide-Semiconductor (DMOS) structure, which has a high switching speed and a high conversion efficiency in the low-voltage region, can realize high breakdown voltage operations and low on-resistances and therefore are widely used as switching elements in motor drivers, power sources, etc., and as analog output elements in audio amplifiers. However, the surface area of the output element unfortunately occupies a large part of the entire chip. To solve this problem, it is necessary to reduce the on-resistance of the DMOS.